The VMware vSphere Web Services API (version 2 and later) offers some methods to manage VMDK files. The VirtualDiskManager managed object defines more than a dozen methods similar to those in the Virtual Disk API documented here.
For more information, navigate to the latest VMware vSphere documentation center on the Web, search for VirtualDiskManager, and follow the specific link. At top of page you can click Local Methods to see a list of all methods defined by the VirtualDiskManager managed object.
VirtualDiskManager methods are not heavily used, and were not updated to support object oriented file systems such vSAN and vVols, nor storage profile based management (SPBM).